The primary long term goal of this research is to develop methods for studying mechanisms of protein association-dissociation reactions. Secondarily, I intend to examine one of the enzymes responsible for glutamate metabolism in the brain in order to determine what factors regulate it. In one of the most common enzyme control mechanisms, changes in activity follow changes in the association state of the enzyme. The generally available techniques for studying this process provide information only about the equilibria involved; the actual mechanisms by which dissociation occurs remain unknown. I propose to study these mechanisms. As with enzyme reactions, dissociation mechanisms could be determined by examining the kinetics of the process. This is not ordinarily possible; proteins usually do not undergo a chemical change when they dissociate. In arginine decarboxylase from Escherichia coli B, however, a single sulfhydryl per subunit becomes available when the decamer dissociates to the dimer. We have begun to develop an approach to the study of dissociation mechanisms which takes advantage of this change in reactivity; we follow arginine decarboxylase dissociation by reaction with 5,5'-dithiobis-(2-nitrobenzoic acid), using a stopped-flow spectrophotometer to obtain initial rates of dissociation. By correlating the observed kinetics with possible dissociation mechanisms and the rate laws derived from them, we have already shown that arginine decarboxylase dissociation is a sequential process in which each step requires the ionization of a single proton, the binding of one Na ion, and an irreversible dissociation reaction. I propose to complete the determination of this dissociation mechanism by defining the role of the substrate, the coenzyme and ionic strength.